It is well-known to design projectiles for fire arms in various ways. This design relates to the structure of the projectile as well as the shape thereof. With structure, reference is made to the construction thereof, i.e., whether the projectile is, e.g., full-jacketed or semi-jacketed as well as the internal design thereof. Usually, a projectile for fire arms comprises a jacket that surrounds, to different extents, a core of preferably lead. Recently, projectiles for fire arms have also begun to be manufactured of other materials than lead, e.g., copper.
The structure of the projectile is most important in hunting, when good shock and depth effect of the game is desired. The shape and structure of the projectile is of significance to the projectile motion in the bore of the barrel of the fire arm, internal ballistics, for the projectile motion in the air, external ballistics, and also for the penetration and motion of the projectile in the target, terminal ballistics.
In all the different known designs mentioned above of a projectile, it has more or less the same basic shape, in that it has the shape of a cylinder having a tapering front end for the formation of the point of the projectile, and a rear end that is cut-off relatively straight or has the shape of a truncated cone for the formation of a boat tail.
During the travel of the bullet through the bore of the barrel, the lands will penetrate and engage the jacket of the projectile to different extents, depending on the type of projectile, in order to provide seal between the jacket/outside of the projectile and the bore as well as to impart rotation to the projectile. Depending on the shape of the projection, either the larger part of the jacket/outside of the cylindrical part of the projectile may form seal against the inside of the bore or only a smaller part, i.e., a so-called power belt of the projectile.
A problem during the travel of the projectile through the bore is that friction arises between the jacket/outside of the projectile and the surfaces in the bore as well as that the jacket/outside in addition is deformed mechanically, when the lands penetrate into the same. This decreases the muzzle velocity of the projectile, which is a disadvantage in respect of the precision as well as the shock effect of a game.
One way to increase the muzzle velocity of a projectile is by changing, e.g., the amount of and/or kind of gunpowder. This can be made within certain limits, but the maximal gas pressure, which the barrel is dimensioned for, must never be exceeded.